Conventionally, as a power transmission device of such type, there is known the one disclosed in Patent Literature 1 for example. The one disclosed therein is directed to a power transmission device to switch a coupled state and an uncoupled state between members which are arranged to be attachable or detachable in a transmission path of a driving force to thereby control transmission of the driving force, and is provided with: a movable plate having ferromagnetic property and provided to be movable forwardly or backwardly between the members, the movable plate advancing to thereby set the coupled state between the members, or alternatively, retracting to thereby set the uncoupled state between the members; permanent magnets which are respectively arranged at an advancing side and a retracting side of the movable plate, each of which generates a magnetic force of attracting the movable plate to thereby hold advancement and retraction of the movable plate; an electromagnet to generate an attraction force of moving the movable plate to be advanced or retracted; a power source mechanism to supply a current to the electromagnet to thereby generate an electromagnetic force so as to move the movable plate to be advanced or retracted by the attraction force which is greater than a holding force with respect to the movable plate exerted by the permanent magnet; and a power control mechanism to control a current to be supplied from the power source mechanism to the electromagnet when the movable plate is moved to be advanced or retracted.
According to such a configuration, a coupled state and an uncoupled state between members are established by holding advancement and retraction of a movable plate by employing a magnetic force of a permanent magnet, and transmission and transmission stop of the driving force can be thereby maintained by only the magnetic force of the permanent magnet. In this manner, power for maintaining the coupled state between the members (transmission of the driving force) and the uncoupled state therebetween (transmission stop of the driving force) is eliminated. On the other hand, a case in which a current is supplied to an electromagnet which takes power consumption is only a case of switching the coupled state between the members (transmission of the driving force) and the recoupled state therebetween (transmission stop of the driving force), and a power source mechanism is controlled so that a power control mechanism supplies a current only in this case. As a result, time to consume power is short, thus making it possible to reduce power consumption of a power transmission device.